1. Field of the Invention
The present invention relates to a vibration sensor and, more specifically, to a vibration sensor for sensing vibrations that is used in a security system of a vehicle.
2. Description of the Related Art
A security system installed in a vehicle, such as an automobile, includes a motion sensor and a shock sensor, which together constitute a vibration sensor apparatus. The motion sensor is adapted to sense a vibration which is composed of a relatively low frequency component and which may be caused when, for instance, a person gets in or out of the vehicle. The shock sensor is adapted to sense a vibration composed of a relatively high frequency component and which may be caused when, for instance, the body of the vehicle is hit, or when the door, the trunk, the bonnet, etc. of the vehicle is opened by force.
However, it is difficult to reduce the size of a security system if it includes a vibration sensor apparatus consisting of a motion sensor and a shock sensor. For this reason, it is desirable that a vibration sensor apparatus for use in a security system of a vehicle consist of a single sensor, and yet be capable of sensing both vibrations composed of high frequency components and vibrations composed of low frequency components. In other words, such a vibration sensor apparatus is desired to be able to sense vibrations of not more than 10 Hz in order to detect a motion with respect to the vehicle, and also able to sense vibrations of from 100 to seven hundred Hz in order to detect a shock applied to the vehicle.